1. Field of the Invention
The present invention relates to a semiconductor laser diode element and a method of manufacturing the same, and more particularly, it relates to a semiconductor laser diode element in which a semiconductor laser diode portion is bonded to a support substrate through a fusion layer and a method of manufacturing the same.
2. Description of the Background Art
A nitride-based semiconductor has a large band gap or high thermal stability and is capable of controlling a band gap width by controlling compositions in growing a semiconductor layer, in general. Therefore, the nitride-based semiconductor is expected as a material allowing application to various semiconductor apparatuses including a laser light-emitting device or a high temperature device. Particularly, a laser light-emitting device employing the nitride-based semiconductor has been put into practice as a light source for pickup corresponding to a large capacity optical disk.
In a case where the nitride-based semiconductor is employed as the laser light-emitting device, a growth substrate difficult to be cleaved such as a hard sapphire substrate is cleaved after reducing the thickness of the substrate by polishing a back surface of the growth substrate since cavity facets are required to be formed by cleavage. However, mass productivity of the laser light-emitting device was not necessarily excellent due to thermal expansion action in polishing or residual stress inside a semiconductor layer after polishing in addition to necessity of a step of polishing the growth substrate.
Therefore, it is generally proposed to form the laser light-emitting device by replacing a nitride-based semiconductor layer formed on a side of the growth substrate with a support substrate easy to be cleaved, as disclosed in Japanese Patent Laying-Open No. 2000-323797, for example.
The aforementioned Japanese Patent Laying-Open No. 2000-323797 discloses a nitride semiconductor laser formed by separating a semiconductor laser diode portion formed on the sapphire substrate from the sapphire substrate and bonding the same to a gallium arsenic substrate easy to be cleaved as a support substrate for replacement and a method of fabricating the same. In this nitride semiconductor laser described in Japanese Patent Laying-Open No. 2000-323797, the gallium arsenic substrate previously adhered with a metal thin film (fusion layer) is bonded to the semiconductor laser diode portion formed on the sapphire substrate, comprising a ridge portion, grooves formed along the ridge portion and support portions formed on a side farther from the ridge portion with the grooves therebetween and having the semiconductor layer with a corrugated surface by application of pressure and heating. Then a short-wavelength high output laser beam such as a YAG laser and a KrF excimer laser is applied to an underlayer from a back surface of the sapphire substrate and the sapphire substrate is separated from the semiconductor laser diode portion after replacement, thereby forming a semiconductor laser.
However, the nitride semiconductor laser and the method of manufacturing the same described in Japanese Patent Laying-Open No. 2000-323797 neither discloses nor suggests how to bring the metal thin film (fusion layer) into contact with corrugated surface of the semiconductor laser diode portion when the gallium arsenic substrate (support substrate) is bonded to the semiconductor laser diode portion. Therefore, it is conceivable that the gallium arsenic substrate is bonded to the semiconductor laser diode portion in a state where the metal thin film is fusion bonded to the projecting ridge portion and the support portions by application of pressure and heating while not being fusion bonded to inner surfaces of the recessed grooves and leaving voids inside the grooves. In this case, when separation of the sapphire substrate (growth substrate) is performed, heat transfer of the void portions left in the grooves of the semiconductor laser diode portion with respect to the gallium arsenic substrate by the laser beam is different from that of portions adhering to the semiconductor layer such as the ridge portion or the support portions and hence temperature variation occurs inside the semiconductor layer. Particularly, heat stays in the voids inside the grooves due to difference in heat transmission coefficient of the peripheral semiconductor layer. Thus, a mechanical property tends to be deteriorated in the semiconductor laser diode portion where temperature variation occurs or heat stays. Consequently, the semiconductor layer is disadvantageously likely to be cracked when the sapphire substrate is separated from the semiconductor laser diode portion.